Lifter Preload Question
08-15-2010, 09:06 PM
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Lifter Preload Question Trying to chase down a low vacuum/surging issue at lower rpms and was wondering if the previous owner put too long of pushrods say .050 out of spec.
Would that be enough to cause the motor to not be able to create enough vacuum?
Would that be enough to cause the motor to not be able to create enough vacuum?
08-16-2010, 06:36 AM
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Yeah thats what I'm doing tonight. I know the car has ls7 lifters and I know the heads have been milled but when I checked the pushrods they're 7.425's.
08-20-2010, 03:35 PM
#5
I believe the LS7 Lifters are about .050" taller in the cup than a LS1 and combined with milled heads I'd say that a 7.350" would be a LOT closer to what you need than 7.425". I use 7.425" on unmilled 5.3L heads with stock lifters. It is the base circle of the cam I'm using that causes the extra .025" needed over stock.
But in the end you MUST measure yourself. A CompCam preload checker from Jegs cost me a whole $11.99 each.
But in the end you MUST measure yourself. A CompCam preload checker from Jegs cost me a whole $11.99 each.
08-20-2010, 04:06 PM
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Very unlikely. In order to cause low vacuum, lifter preload would need to bottom-out the lifter and prevent the valve (or valves) from fully closing. Preload needs to be more than 0.050 off to do that.
